Beauveria bassiana: as a potential microbial biocontrol agent for tea mosquito bug, Helopeltis theivora Waterhouse (Hemiptera: Miridae) in Dooars and Darjeeling, India

Background In the present study, the efficacy of two isolates of Beauveria bassiana namely, BKN20 and BKN1/14 was evaluated against the tea mosquito bug (TMB), Helopeltis theivora, Waterhouse (Hemiptera: Miridae) damaging harvestable shoots of tea plants in the Dooars and Darjeeling regions of West Bengal, India. Results Laboratory study revealed that, in both isolates, BKN20 was more pathogenic than BKN1/14, exhibiting 76% mortality of the test insect. The BKN20 isolate was formulated as an aqueous suspension (5%AS), and evaluated against TMB through micro-plot trials in tea plantations. The Micro-plot field study revealed a maximum of 72.19% reduction in the shoot damage due to TMB in plots sprayed with a 1000 ml/ha concentration of BKN20 5%AS containing 2 × 107 conidia/ml, as compared to the synthetic insecticide (Thiamethoxam 25%WG), where a 63.12% reduction in the shoots was recorded. Furthermore, different concentrations of the formulated BKN20 5%AS were evaluated against the test insect at 2 locations of tea gardens in the Dooars and Darjeeling regions. The results from both locations revealed that 1000 and 1200 ml/ha concentrations of BKN20 5%AS (each concentration containing 2 × 107 conidia/ml) significantly (p < 0.05) reduced the TMB population and they were more effective than Thiamethoxam 25%WG (120 g/ha). However, non-significant differences in crop yields were recorded. The formulation BKN20 5%AS was found to be non-pathogenic to non-target insects, i.e. natural enemies present in the tea ecosystem. BKN20 5%AS had no phytotoxic effect on the tea leaves, with acceptable organoleptic attributes. Conclusion The BKN20 isolate could be commercialized as an alternative microbial insecticide to reduce the load of chemical insecticides in the tea ecosystem.

Prevalence of insect pests in large cardamom (Amomum subulatum Roxb.) and evaluation of bio-rationals for the management of major pests under organic agro-ecosystem of Sikkim

Large cardamom (Amomum subulatum Roxb.) is one of the important cash crops of Sikkim and Darjeeling areas of West Bengal. In this study, a fixed plot survey on insect pests of large cardamom was conducted and found that stem borer (Glyphipterix spp., Lepidoptera: Glyphiperidae), shoot fly (Merochlotops dimorphus Cherian, Diptera: Chlororpidae), leaf eating caterpillar (Artona chorista Jordon, Lepidoptera: Zygaenidae) and tea mosquito bug (Helopeltis theivora Waterhouse, Hemiptera: Miridae) are the major pests of the crop. Eco-friendly organic treatments like neem-based oil, petroleum-derived horticultural oil, spinosad and different formulations of entomopathogens were tested against these major insects. Among all, application of spinosad 45 SC @ 0.3 ml L-1 was found effective followed by neem-based oil (Azadirachtin 0.15% EC) 1500 ppm @ 3 ml L-1 at three different time intervals (first application in February-March, second application in June-July and third application in October-November) against all insects. Moreover, entomopathogenic bio-control agents (Bacillus thuringiensis @ 2 ml L-1, Metarhizium anisopliae@ 5 ml L-1 and Beauveria bassiana @ 5 ml L-1) were on par with neem-based oil for the management of stem borer. Considering the economic importance of the crop and absence of valid technology for management of insect pests in large cardamom through organic options, application of either of them could be helpful in organic management of insect pests in Sikkim.

Biology, feeding and oviposition preference of Helopeltis theivora, with notes on the differential distribution of species of the tea mosquito bug species complex across elevations

Cocoa (Theobroma cacao L.) is an important beverage crop and commercially grown as a plantation crop. With the changing climate, the tea mosquito bug species complex, viz., Helopeltis theivora, H. bradyi and H. antonii, is emerging as a major threat to cocoa cultivation in India. Among the species of this complex H. theivora is responsible for causing considerable damage. The present investigations were carried out to find a weak link in the life cycle of H. theivora so it can be managed effectively. Specimens of the tea mosquito bug were found to first appear during the first week of September in South India. Helopeltis theivora requires on average 29.28 days to complete its life cycle on cocoa. The highest level of natural mortality was recorded in the first-instar nymph. The total developmental period of the fifth-instar nymph was significantly longer than that for the other nymphal instars. The sex ratio reflects that the population is highly female-biased, which may contribute to the dominant nature of this species in the cocoa ecosystem. Observation of the feeding and oviposition behavior of H. theivora revealed that the insect prefers to feed and oviposit on developing pods rather than on leaves and shoots. Analysis of the species distribution of tea mosquito bug at different elevations revealed that cocoa gardens situated less than 300 meter above mean sea level are dominated by H. theivora, whereas gardens situated more than 300 meter above mean sea level are dominated by H. bradyi. This separation of species across elevation may be driven either by abiotic or biotic factors.